Aeryl terpolymers as binders for electrophotographic compositions

ABSTRACT

An electrophotographic copying material comprising a support and a photoconductive layer formed on one surface of said support, said photoconductive layer being formed in such a way that a photoconductive layer-forming solution-which is prepared by dispersing a photoconductive substance in an aqueous emulsion containing an acryl resin emulsified in water with an emulsifier consisting of an acidic compound and a volatile basic compound-is coated onto one surface of said support and then dried.

United States Patent Tubuko et al.

AERYL TERPOLYMERS AS BINDERS FOR ELECTROPHOTOGRAPHIC COMPOSITIONS Inventors: Kazuo Tubuko; Nario Yamaguchi; Sakae Shimizu, all of Tokyo, Japan Assignees Kabushiki Kaisha Ricoh, Tokyo, Japan Filed: Dec. 11, 1968 Appl No.: 783,118

Foreign Application Priority Data Dec. 18, 1967 Japan ..42/80667 US. Cl ..96/1.5, 96/1.8, 260/29.6, 1 17/201 Int. Cl. ..G03g 5/08 ..96/l.51.8; 117/201; 260/296 References Cited UNITED STATES PATENTS Re. 25.44 9/1963 Kucera ..96/l 8/1961 Tannenbaum ..96/ 1 Mar. 14, 1972 Primary Examiner-George F Lesmes Assistant Examiner]ohn C. Cooper, 111 AttorneyWoodhams, Blanchard and Flynn [57] ABSTRACT An electrophotographic copying material comprising a support and a photoconductive layer formed on one surface of said support, said photoconductive layer being formed in such a way that a photoconductive layer-forming so1utionwhich is prepared by dispersing a photoconductive substance in an aqueous emulsion containing an acryl resin emulsified in water with an emulsifier consisting of an acidic compound and a volatile basic compound-is coated onto one surface of said support and then dried.

5 Claims, No Drawings AERYL 'IERPOLYMERS AS BINDERS FOR ELECTROPHOTOGRAPHIC COMPOSITIONS BACKGROUND OF THE INVENTION a. Field of the invention The present invention relates to an electrophotographic copying material produced by forming a photoconductive layer on the surface of a support with a binder consisting of an oil-in-water-type emulsion prepared by dispersing resinous binder solution drops in water, and to the method of manufacturing thereof.

b. Description of the prior art In the past, as for the material of photoconductive layer of an electrophotographic copying material, metallic oxides such as zinc oxide, titanium oxide, and the like were mainly used as a photoconductive substance for said purpose. Meanwhile, as for the resinous binder to fix the photoconductive substance onto a support (consisting of paper or a plastic film whose surface resistance is less than lO Q-cm.), those resins which have a high electric resistance and are soluble in organic solvents were generally used. However, the aforesaid materials involve such risks as causing bodily injury om'ng to the poisonous vapor of said organic solvents or dangerous explosions owing to the inflammability thereof, because the formation of said photoconductive layer requires dissolution and dispersion of said photoconductive substance and resinous binder into an organic solvent. Consequently, costly equipment is necessary to cope with such eventual hazards under present techniques.

From the standpoint that the aforesaid risks will be avoided if the resinous binder were water soluble or water dispersive, a variety of water-dispersive resinous binders have been proposed in the past. However, the electrophotographic copying material produced in accordance with prior processes had drawbacks with respect to its electrostatic characteristics; for instance, the electric potential charged by corona discharge was relatively low and the retention of electric potential in case of said material being left in a dark place after being charged, that is, the dark-decay, was great, and accordingly, was far from satisfactory for practical use.

The present invention provides an electrophotographic copying material which is by no means inferior in terms of its electrophotographic characteristics to any electrophotographic copying material in the prior art, by employing a water-dispersed resinous binder instead of the heretofore conventional organic-solvent soluble resinous binder.

1n the present invention, there are employed specific acryl resins and specific emulsifiers. To be precise, the resins to be employed as the binder in forming a photoconductive layer include solvent soluble type acryl-resins having an acid reaction, i.e., acid value, which are obtained by the copolymerization of acryl-resin and at least one monomer selected from the group consisting of unsaturated monocarboxylic acids such as crotonic acid, itaconic acid, acrylic acid, and methacrylic acid, unsaturated dicarboxylic acids such as maleic acid and fumaric acid, and monoesters of said dicarboxylic acids such as methylester, ethylester, propylester, monobutylester, and monolaurylester. And as for the emulsifier to be employed for emulsifying these acryl-resins in water, such emulsifiers as the following are applicable.

a. An emulsifier consisting of a natural resin which has an acid value and a high electric resistance (more than 10"!!- cm.) and a volatile basic compound.

b. An emulsifier consisting of a synthetic resin which has an acid value and a high electric resistance (more than 10!!- cm.) and a volatile basic compound.

c. An emulsifier comprising at least one carboxylic acid selected from the group consisting of an alicyclic compound having a carboxyl radical, an aliphatic carboxylic acid, and an aromatic carboxylic acid, as well as a volatile basic compound.

As for an acid compound, i.e., a natural resin containing a resin acid, to be employed for the aforesaid (a) member, such a resin as having electric resistance of at least l0"Q-cm. is selected lest its special quality should be deteriorated when applied in a photoconductive layer. Natural resins having such a property and considered suitable for application include, for example, elemi, Gurjun balsam, jalap, scammonia, amber, bdellium, sagapenum, Euphorbium, myrrh, Opopanax, various kinds of dammar (such as Benak, dead dammar, Melanty, Chan, yon banoun, papuan dammar), shellac, acaroid, dragon brad, mustic, styrax, canada balsam, mecca balsam, copaiba balsam, Peru balsam, guaiac, tacamahac, galvanum, gamboge, olibanum, ammoniac, asafetida, various kinds of copal (such as kauri copal, soft manila copal, hard manila copal, congo copal, benguela copal, angora copal, madagascar copal, zanzibar copal, demera copal, hard bomea copal, new zealand kauri copal), various kinds of rosin (such as gum rosin, heterogeneous rosin, polymerized rosin, hydrogenated rosin, tall oil, rosin malate, rosin oxide, hardened rosin, ester gum), benzoic acid, sandarack, true balsam, and kawakawa resin. Various manufactures whose principal component falls within such sorts as enumerated above are available on the market under different trade names.

Acid compounds for (0) member, i.e., carboxylic acids of alicyclid compounds, include, for example, abietic acid, bisnorcholanic acid, B-boswelic acid, chenodesoxylcholic acid, chenobic acid, cholanic acid, Cholic acid, dehydrocholic acid, dioxylcoal acid, doisynolic acid, erythrophleinic acid, etiocholanic acid, glycocholic acid, glychyrrhizic acid, oleanolic acid, helvolic acid, hiodesoxycholic acid, isocholic acid, naphthenic acid, norcholanic acid, e-pimaric acid, quillaic acid, ursodesoxycholic acid, and ursolic acid.

Acid compounds for (c) member, i.e., an aliphatic carboxylic acid, an aromatic carboxylic acid, and an acid anhydride of said carboxylic acids, include so many applicable acids as enumerated as follows:

aliphatic saturated monocarboxylic acid:

caproic acid, heptanoic acid, caprylic acid, pelargonic acid,

capric acid, n-undecylenic acid, lauric acid, ntridecylenic acid, myristic acid, n-pentadecylenic acid, palmitic acid, margaric acid, stearic acid, nnonadecylenic acid, arachidic acid, n-heneioosanoic acid, behenic acid, n-tricosanoic acid, lignoceric acid, n-pentacosanoic acid, ceratic acid, n-heptacosanoic acid, montanic acid, n-nonacosanoic acid, melissic acid, n-hentriacontanoic acid, n-dotriacontanoic acid, ntetratriacontanoic acid, ceroplastic acid, n-hexatriacontanoic acid, n-octatriacontanoic acid and n-hexatetracontanoic acid.

aliphatic olefin monocarboxylic acid:

2-hexenoic acid, 3-hexenoic acid, 4-hexe'noic acid, S-hexenoic acid, 2-methyl-2-pentenoic acid, 3-methyl-2-pentenoic acid, 4-methyl-2-pentenoic acid, 4-methylpentenoic acid, a-ethylcrotonic acid, 2,2-dimethyl-3-butenoic acid, 2-heptenoic acid, 2-octenoic acid, 4 decenoic acid, 9-decenoic acid, 9-undecenoic acid, IO-undecenoic acid, 4-dodecenoic acid, S-dodecenoic acid, 4- tetradecenoic acid, 9-tetradecenoic acid, 9-hexadecenoic acid, 2-octadecenoic acid, cis-6-octadecenoic acid, 9-octadecenoic acid, oil acid, elaidic acid, ll-octadecenoic acid, l2-octadecenoic acid, 9-eicosenoic acid, lleicosenoic acid, ll-docosenoic acid, l3-docosenoic acid, erucic acid, l5-tetracosenoic acid and mycolipenic acid. aliphatic diolefin carboxylic acid:

2,4-hexadienoic acid, diallylacetic acid, geranium acid and 2,4-decadienoic acid.

aliphatic higher unsaturated monocarboxylic acid:

hexadecatrienoic acid, linoleic acid, linolenic acid, 6.9.l2-

octadecatrienoic acid, eicosadienoic acid, eicosatrienoic acid, decosadienoic acid, decosatrienoic acid and heracodienoic acid.

aliphatic saturated dicarboxylic acid:

adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane dicarboxylic acid, dodecane dicarboxylic acid, brassylic acid and tetradecane dicarboxylic acid. aromatic monocarboxylic acid:

benzoic acid, o-toluylic acid, rn-taluylic acid, p-toluylic acid, dimethylbenzoic acid, o-ethylbenzoic acid, m-ethylbenzoic acid, p-ethylbenzoic acid, 2.3.4-trimethylbenzoic acid, 2.3.5-trimethylbenzoic acid, 2.3.6-trimethylbenzoic acid, 2.4.5-trimethyl-benzoic acid, 2.4.6-trimethylbenzoic acid, 3.4.S-trirnethylbenzoic acid, cuminic acid, cinnamic acid, o-nitrobenzoic acid, m-nitrobenzoic acid, p-

nitrobenzoic acid, 2.4-dinitrobenzoic acid, 3.5- dinitrobenzoic acid, o-chlorobenzoic acid, pchlorobenzoic acid, o-fluorobenzoic acid, m-

fluorobenzoic acid, p-fluorobenzoic acid, o-bromobenzoic acid, m-bromobenzoic acid,

p-bromobenzoic acid, o-iodobenzoic acid, m-iodobenzoic acid, p-iodebenzoic acid, 2.3-dichlorobenzoic acid, 2.5-

dichlorobenzoic acid, 2.6-dichlorobenzoic acid, 3.4- dichlorobenzoic acid, 3.5-dichlorobenzoic acid, 2.3- dibromobenzoic acid, 2.4-dibromobenzoic acid, 2.5- dibromobenzoic acid, 2.6-dibromobenzoic acid, 3.4- dibromobenzoic acid, 3.5-dibromobenzoic acid, 2.3- diiodobenzoic acid, 2.4-diiodobenzoic acid, 2.5- diiodobenzoic acid, 2.6-diiodobenzoic acid, 3.4-

diiodobenzoic acid, 3.5-diiodobenzoic acid, 2-chloro-5- nitrobenzoic acid, 3-chloro-6-nitrobenzoic acid, 2-

bromo-S-nitrobenzoic acid, Z-chIoro-cinnamic acid, 2- cyano-cinnamic acid, Z-naphthaoic acid, 5- chloronaphthoic acid, B-naphthoic acid and 5- bromonaphthoic acid. Aromatic dicarboxylic acid: phthalic acid, isophthalic acid, terephthalic acid, 3-

chlorophthalic acid, 4-chlorophthalic acid, 3.6- dichlorophthalic acid, tetrachlorophthalic acid, tetrabromophthalic acid, tetraiodophthalic acid, naphthalic acid, naphthaline-l,Z-dicarboxylic acid,

naphthalin-l,4-dicarboxylic acid and naphthalin-l,5- dicarboxylic acid.

Aromatic tricarboxylic acid:

1,2,3-hemirnellitic acid and 1,2,4-trimellitic acid.

As for synthetic resins having an acid value, which are to be employed for (b) member such a synthetic resin as having electric resistance of at least l0"O.-cm. is selected for the same reasons as in the case of (a) member in the foregoing. Therefore, the suitable synthetic resins include, for example, copolymer resins of acrylic ester, acryl-alkyd resin, pure alkyd resin, epoxy ester resin, nondrying-type pure alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, natural resin-modified phenolic resin, natural resin-modified maleic acid resin, natural resinmodified pentaerythritol resin, natural resin-modified fumaric acid resin, and so forth.

Moreover, as for the volatile basic compound which is the fellow component of the aforesaid emulsifier (a), (b), and (c), a nitrogen containing compound such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, hexylamine, ethylendiamine, arylamine, morpholine, piperazine, and hydrazine is suitable.

Those solvent soluble type resins on the market can be made to emulsify in water by means of an acidic compound such as natural resins containing resin acid, synthetic resins having an acid value, carboxylic acid of alicyclic compound and aromatic carboxylic acid; and aforesaid basic compound such as ammonia, morpholine, primary amine, secondary amine, and tertiary amine; and these emulsified resins are suitable for use as binders for photoconductive layer-forming materials of electrophotographic copying materials. However, as a result of the comprehensive and intensive examinations of the aforesaid resins in further close relation to the electrostatic characteristics as well as the electrophotographic copying character conducted by the inventors of the present invention, it has been discovered that the acrylic copolymer containing carboxylic acid is most readily emulsified and is exceedingly suitable as a binder for photoconductive layer-forming materials. it was also found that, among said acrylic copolymer resins, such a resin that is at least a ternary copolymer and whose acid value is 2 or more is preferable as the binder for said photoconductive layer-forming material, and this finding led to the present invention. Meanwhile, it was also discovered that any acryl-resin which contains no carboxylic acid has a poor emulsive character, and is therefore unsuitable for use as a binder. As seen in the foregoing, although the cause of such fact that an acrylic resin copolymer containing a carboxylic acid has such advantages required for a binder as stated above is yet to be clarified, said advantages may be mainly attributable to the fact that the particles of resin become an O/W-type emulsion by forming a stable hydrated-layer upon forming the emulsification. Moreover, it is noted that although the more quantity of carboxylic acid is contained in the acrylic copolymer, the higher is the emulsive character of said copolymer, the employment of an excessive quantity thereof will result in deterioration of the electrostatic characteristics of the layer of the copying material produced. Therefore, according to the present invention, such a copolymer whose acid value in within the range of 2-100 is considered most suitable.

The acryl-resin to be employed in fixing a photoconductive layer of the copying material of the present invention is a copolymer which contains, through copolymerization, at least one ester selected from the group consisting of acrylic esters and methacrylic esters, In other words, in the present invention, there are employed not only such a copolymer that is obtained by copolymerizing said ester with at least one member selected from the group consisting of unsaturated carboxylic acids such as aforesaid crotonic acid, maleic acid, itaconic acid, fumaric acid, acrylic acid and methacrylic acid, and monoesters of unsaturated dicarboxylic acids; but also such a copolymer that is obtained through copolymerization with such polymerizing monomers as acrylonitrile, methacrylonitrile, styrene, dichlorstyrene, vinyl acetate, vinyl chloride, and vinylidene chloride with aforesaid copolymer. Among said copolymers, as for the copolymers combined with a carboxylic acid, a copolymer converted to an amido-compound by bonding an amino radical with a portion of said carboxylic acid, a copolymer obtained by bonding a methylol radical with a portion of said carboxylic acid, and a copolymer converted to a salt by applying a basic substance such as acrylamide, methacrylamide, methylolacrylamide, hydroxyethyl methacrylate, hydroxybuthylacrylate, trimethylamine salt and triethylamine salt can also be employed.

The quantity of acrylic ester and/or methacrylic ester contained in these copolymers is preferred to be 50-95 weight percent. As for the ester, one that is obtained by applying alcohol having one to four carbon atoms to acrylic acid or methacrylic acid is most suitable. In case where a higher alcohol is applied in obtaining ester of higher alcohol, it is advisable to resort to the ester interchange reaction between a ester of lower alcohol and higher alcohol.

Such copolymerized acryl-resins as employed in the present invention have already been made commercially available. There are, for instance, two products of TElKOKU KAGAKU Co. named Acryl Resin SBIlC (acid value: 15) and Acryl Resin SBISSM (acid vaiuezlS), a product of FUJIKURA KASEI Co. named Camel (acid valuezl4), and a product of DAINIPPON INK and Chemicals Co, Ltd., named Acryl Resin Lustrasol ODA-l l 1-40 (acid vaJue:3.5). Besides, other acryl-resins having almost the same character as that of the foregoing materi als have also been put on the market by NIHON GOSEI KAGAKU Co., TOA GOSEI KAGAKU Co., etc.

In the emulsification of the aforesaid resinous binder into an aqueous solution containing the aforesaid emulsifier, it is preferable to mix parts by weight of the former, i.e., resinous binder with 1-20 parts by weight of the latter, i.e., the emulsifier. And, as for the ratio of acidic compound to the volatile basic compound contained in said emulsifier, it is desirable that the parts by weight of the latter be 0.5-5 to 1 part by weight of the former. lnto the emulsion thus obtained are added the powder of photoconductive substance and preferably a sensitizer (such as phthalein dye, triphenylmethane dye, cyanine dye, heterocyclic dye, and one or more than two mixtures of these dyes). Then, the photoconductive layer forming solution thus obtained is coated on the surface of a support by such methods as the spray coating method, centrifugal coating method, and brush coating method, and thereafter the emulsion on said surface is dried by the hot-air drying method or by the infrared-ray drying method, and thereby the novel electrophotographic copying material is produced. According to this method of manufacturing of copying material, one component of the emulsifier, that is, the volatile basic substance, is to be evaporated in the course of the drying, so that there is no risk that the efficiency of the photoconductive layer formed on the support will be deteriorated by said basic substance. In this regard, however, it is noted that the existence of residues of said volatile basic substance in the photoconductive layer to the extent not exceeding 0.5 percent of the total weight of said photoconductive layer would not be harmful. As for the temperature required for the aforesaid drying method to be employed for evaporation of said volatile basic substance, it is desirable to be in the range of 100250 C.

In the light of the foregoing, the electrophotographic copying material of the present invention, which consists of a support whose surface is provided with a photoconductive layer comprising a photoconductive substance prepared by employing above-stated emulsified binder, is possessed of all the characteristics required for an electrophotographic copying material, such as that it exhibits a satisfactory electric chargeability when impressed with an electric charge by corona discharge, shows a low degree of dark-decay when placed in a dark place after impressed with an electric charge, and is conspicously rapid in decreasing of electric potential due to exposure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I In this example, 3 g. of Stebelite Resin (a denatured natural resin containing hydrogenerated rosin with acid value 40, manufactured by Hercules Powder Co., U.S.) was added to 70 g. of an acryl-resin (acid value:l5) containing carboxylic acidthis resin consists 40 parts by weight of butylacrylate, 20 parts by weight of styrene, 36 parts by weight of methyl methcrylate, and 4 parts by weight of acrylic acid-and dissolved by heating at 50 C. A solution thus obtained was agitated by a homomixer while another solution, which had been prepared by dissolving 3 g. of triethylamine in 100 g. of water, being added thereto steadily, and said resin was emulsified thereby. Next, 100 g. of photoconductive zinc oxide and 100 g. of water were added to 80 g. of the emulsion thus obtained, and the resultant mixture was further agitated by a homomixer. After that, 3 cc. of a sensitizer (i.e., a methanol solution comprising 1 percent each of Rose Bengal and Fluorescein dissolved therein) was added to thus processed emulsion, and thereby was produced a photoconductive layerforrning solution. Subsequently, said photoconductive layerforrning solution was coated on the surface of an art paper whose back had been processed for conductivity, and was dried at 120 C. for min, and an electrophotographic copying material was produced thereby. The electrostatic characteristics of a copying material thus produced are quite satisfactory, and, in fact, formed a highly concentrated and clear copied image when put to practical use for copying.

Even where Acryl Resin SBI 1C (a manufacture of TEIKOKU KAGAKU Co.) is substituted for the aforesaid acryl-resin, quite the same effect as the above will be obtained.

On the other hand, for the sake of comparison in respect of the efficiency and performance of copying materials, another acryl-resin which does not contain any carboxylic acid, a thermoplastic resin, and a therrnosetting resin were, respectively, employed for producing an emulsion through the same processes as of the present invention. However, each of those substitute resins was very poor in its emulsification ability, and some of the copying materials which were produced by employing said resins in forming a photoconductive layer thereon had such drawback as causing cracks in its layer, and the image-making ability thereof was quite poor when used for copying. Also, those copying materials which were produced in the same way as above by employing such an emulsion that was obtained by emulsifying acryl-resins or vinyl acetate resins by means of the anion-type, cation-type, or nonion-type surface active agent put on the market, produced no copied image whatsoever when used for copying. Example 2 In this example, 3 g. of naphthenic acid was added to 100 g. of an acryl resin (acid valuez8) containing carboxylic acidthis resin consists 70 weight percent of ethylacrylate, 27 weight percent of styrene, and 3 weight percent of maleic acid and agitated by a homomixer while another solution, which had been prepared by dissolving 3 g. of morpholine into 100 g. of water, being added thereto steadily, and said resin was emulsified thereby. Next, 100 g. of zinc oxide and I00 g. of water were added to 80 g. of the emulsion thus obtained, and further a sensitizer (comprising 0.05 g. of Bromophenol Blue and 0.03 g. of Rose Bengal) was added thereto. The mixture thus obtained was agitated by a homomixer to get dispersed thoroughly, and thereby a photoconductive layerforming solution was produced. Subsequently, said photoconductive layer-forming solution was coated on the surface of a support the same one as that in Example I and was dried, and an electrophotographic copying material was obtained thereby. The concentration of the copied image exhibited by said copying material, when measured on actual perfonnance, was 1.2. Said value of image concentration was attained by using a densitometer (NARUMI Densitometer manufactured by NARUMI SI-IOKAI Co., Japan). Example 3 In this example, 100 g. of acryl-resin (acid value2l4) containing carboxylic acid-- this resin consists weight percent of styrene, 10 weight percent of acrylonitrile, 25 weight percent of isopropylacrylate, and 5 weight percent of acryl acid 0.5 g. cobalt naphthenate, and 0.5 g. of p-chlorobenzoic acid were mixed and agitated by a homomixer while another solution, which had been prepared by dissolving 3 g. of trimethylamine into 100 g. of water, being added thereto steadily, and said resin was emulsified thereby. Next, I00 g. of zinc oxide and a sensitizer (comprising 0.03 g. of Rose Bengal and 0.05 g. of Bromophenol Blue) were added to 90 g. of the resultant emulsion and thoroughly agitated, whereby obtaining a photoconductive layer-forming solution. The photoconductive layer-forming solution thus prepared was coated on the surface of a support the same one as that in Example I- and was dried, and an electrophotographic copying material was obtained thereby. The electrostatic characteristics of thus obtained copying material were equivalent to that of Example 1 of this invention. In particular, the saturated electric potential at the time when an electric charge was impressed into its photoconductive layer by corona discharge came up to 35 V./p., the degree of its dark-decay was low, and its employment in copying brought about a clear copied image having a high concentration.

Meanwhile, for the sake of comparison in respect of the efficiency and performance of copying materials, another copying material was prepared by employing an emulsion of acrylresin, which has been put on the market as a sort of emulsified substance (i.e., AB- 1 2 manufactured by TEIKOKU KAGAKU Co.) and was used in copying. However, no copied image was formed by said material. Furthermore, in case where a silicone resin was processed for emulsification in the same way as in the present invention, the emulsification ability of said resin was so poor that the image-making performance of the copying material produced by employing said resin was also unsatisfactory.

Example 4 ln this example, 100 g. of acryl-resin (acid value:3.5 which consists 1.5 weight percent of methacrylic acid, 38.5 weight percent of butyl methacrylate, 50 weight percent of styrene, and weight percent of hydroxypropylacrylate- 3 g. of stearic acid, 100 g. of water, and 3 g. of morpholine were employed to prepare an emulsion containing said resin thus emulsified. Then, by adding 100 g. of zinc oxide, sensitizer (comprising 0.05 g. of Rose Bengal and 0.05 g. of Fluorescein), and 100 g. of water to 80 g. of the aforesaid emulsion, a photoconductive layer-forming solution was prepared. Subsequently, the same processes as in Example 1 were followed and an electrophotographic copying material was obtained thereby. The electrostatic characteristics of thus obtained copying material and its image-making performance exhibited in actual copying were equivalent to that of Example 1 of the present invention.

We claim:

1. The method of preparing an electrophotographic copying material comprising an electroconductive support having on one surface a photoconductive film layer, the said material capable of assuming and retaining an image-forming electrostatic charge, which method comprises forming an aqueous, oil-in-water emulsion of a resinous binder consisting of an acryl resin having an acid value in the range of from 2 to 100 and prepared by copolymerizing (1) from about 50 to about 95 weight percent of at least one ester selected from the group consisting of alkylacrylates and alkylmethacrylates in which the alkyl has from one to four carbon atoms, (2) at least one monomer selected from the group consisting of unsaturated monocarboxylic acids, unsaturated dicarboxylic acids and monoesters of said unsaturated dicarboxylic acids and ('3') at least one vinyl monomer selected from the group consisting of acrylonitrile, methacrylonitrile, styrene, dichlorostyrene, vinyl acetate, vinyl chloride and vinylidene chloride; (4) at least one carboxyl-containing emulsifier dispersed in said resinous binder and selected from the group consisting of a natural resin having a resin acid and an electric resistance not less than 10"Q-cm., a synthetic resin having an acid reaction and an electric resistance not less than 10"!!- cm., alicyclic compounds having a carboxyl radical, aliphatic carboxylic acids and aromatic carboxylic acids; and

an inorganic photoconductive substance dispersed in said resinous binder, by emulsifying said resinous binder in the presence of said acidic compound and in an aqueous solution of a volatile base as sole emulsifying agent, applying a film of said emulsion to said conductive support and drying said film for a time sufficient to evaporate substantially all of said volatile base.

2. The method of claim 1 in which the volatile base is a member of the group consisting of ammonia, methylamine, dimethylarnine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, hexylamine, ethylenediamine, arylamine, morpholine, piperazine and hydrazine, and said volatile basic compound being present in said layer within a range not exceeding 0.5 percent per total weight of said photoconductive layer.

3. An electrophotographic copying material prepared by the process of claim 1.

4. An electrophotographic copying material according to claim 3, wherein said synthetic resin having an acid reaction is selected from the group consisting of an acryl-alkyd resin, pure alkyd resin, epoxy ester resin, nondrying-type pure alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, natural resin-modified phenolic resin, natural resin-modified maleic acid resin, natural resinmodified pentaerythritol resin and natural resin-modified fumaric acid resin.

5. An electrophotographic copying material according to claim 3, wherein said natural resin is selected from the group consisting of elemi, gurjun balsam, jalap, scarnmonia, amber, bdellium, sagapenum, euphorbium, myrrh, opopanax, shellac, acaroid, dragon brad, mustic, s rax, canada balsam, mecca balsam, copaiba balsam, peru ba am, guarac, tacamahac, galvanum, gamboge, olibanurn, ammoniac, asafetida, copals, sandarack, true balsam and kawakawa resin. 

2. The method of claim 1 in which the volatile base is a member of the group consisting of ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, hexylamine, ethylenediamine, arylamine, morpholine, piperazine and hydrazine, and said volatile basic compound being present in said layer within a range not exceeding 0.5 percent per total weight of said photoconductive layer.
 3. An electrophotographic copying material prepared by the process of claim
 1. 4. An electrophotographic copying material according to claim 3, wherein said synthetic resin having an acid reaction is selected from the group consisting of an acryl-alkyd resin, pure alkyd resin, epoxy ester resin, nondrying-type pure alkyd resin, rosin-modified alkyd resin, phenol-modified alkyd resin, styrenated alkyd resin, natural resin-modified phenolic resin, natural resin-modified maleic acid resin, natural resin-modified pentaerythritol resin and natural resin-modified fumaric acid resin.
 5. An electrophotographic copying material according to claim 3, wherein said natural resin is selected from the group consisting of elemi, gurjun balsam, jalap, scammonia, amber, bdellium, sagapenum, euphorbium, myrrh, opopanax, shellac, acaroid, dragon brad, mustic, styrax, canada balsam, mecca balsam, copaiba balsam, peru balsam, guaiac, tacamahac, galvanum, gamboge, olibanum, ammoniac, asafetida, copals, sandarack, true balsam and kawakawa resin. 